Intervertebral prostheses need to be fixed to the adjacent vertebral bodies in order to ensure that they do not shift from the position assigned to them. It is known to provide them with ribs or studs which are fitted into correspondingly shaped fixing recesses in the cover plates of the vertebral bodies (WO 01/01893, WO 2004/080355, DE-3023353, FR-A-2659226). Producing these requires deep working of the cover plates of the vertebral bodies, which entails considerable outlay in operating terms. Such working of the cover plates of the vertebral bodies is also undesirable, and in the area of the cervical spine often impossible, because it demands considerable distraction and presupposes a substantial thickness of the vertebral bodies.
Particularly for the cervical spine, prosthesis structures are therefore preferred which do not demand the formation of fixing recesses in the cover plates of the vertebral bodies. These prosthesis structures include prostheses in which the outer faces of the attachment plates have a transversely extending toothed arrangement covering more or less the whole surface area and with a sawtooth profile whose steep flanks are arranged ventrally (WO 2004/089259, FR-A-2718635). Although a displacement of the prosthesis in the ventral direction can normally be prevented by this means, cases nevertheless occur where, because of unusual anatomy or unsuitable surgical preparation, the intervertebral space opens out in such a pronounced wedge shape in the ventral direction that the prosthesis cannot be securely held in place by the toothing alone. This is because the toothing does not penetrate into the bone surface. It is not intended to do so, in order not to extensively damage and thus weaken the cortical bone. Instead, it is intended to bear on the bone surface, which in normal circumstances is adequate to ensure fixation, since it then also secures itself on surface irregularities.
Intervertebral prostheses with self-tapping fixing projections are also known (EP-A-1057462, EP-A-1103237). The outer face of the attachment plates of the prosthesis forms an attachment surface for connection to the vertebral body. It comprises a base surface which is intended to bear on the bone surface, and fixing projections which rise from the base surface and which are so sharp that, under the natural loading of the articulation, and by means of the force of the ligaments and the transmitted weight, they penetrate into the bone surface as soon as the distraction of the vertebral bodies is cancelled. However, the known prostheses of this kind require considerable distraction to ensure that they are not impeded by the fixing projections when fitted into place. This can in some cases be tolerated in the region of the lumbar spine and thoracic spine, but not in the region of the cervical spine. If they were to be pressed in without sufficient distraction, the fixing projections would carve out channels in the cover plates of the vertebral bodies, and they could then slide out again through these channels, in addition to which the channels are undesirable because of the loss of strength they entail.